1. Field of the Invention
The present invention relates to a method of sealing a semiconductor element with resin and a vacuum type resin-sealing apparatus and a long size lead frame for use in the method.
2. Description of the Background Art
FIG. 1 is a cross-sectional view showing a conventional vacuum type resin-sealing apparatus which includes a cope 1 and a drag 10 disposed on opposite sides of a parting plane A--A. FIG. 2 is a plan view showing the drag 10 viewed from the parting plane A--A. Referring to FIG. 1, the cope 1 comprises a rectangular upper wall 2 and an upper cavity block 3 provided on the underside of the upper wall 2. The upper cavity block 3 is provided with a number of recesses or cavities 4A arranged in two rows. On the underside of the upper wall 2, a circular upper seal block 5 is also provided to surround the upper cavity block 3. The upper seal block 5 is provided with a vacuum air outlet 6 which penetrates the upper seal block 5 and is connected with a vacuum equipment 40 such as a vacuum pump. The upper seal block 5 is also provided on the upper wall 2 side surface thereof with a sealant 7A of silicone rubber or `Teflon`. A chamber wall 8A penetrates the upper wall 2 and the cavity block 3 to form a chamber 8. The chamber wall 8A is fixed by means of a flange 9. A sealant 7B around the chamber wall 8A is provided between the upper wall 2 and the chamber wall 8A. Thus, the cope 1 is structured.
The cross section of the drag 10 of FIG. 1 is taken along line B--B of FIG. 2. The cross section of the cope 1 of FIG. 1 is also taken along line B--B of FIG. 2 except for the chamber 8 and the neighborhood thereof, the cross section of which is taken along line C--C of FIG. 2.
The drag 10 comprises a rectangular lower wall 11 and a lower cavity block 12 provided on the top surface of the lower wall 11. The lower cavity block 12 is provided with a number of recesses or cavities 4B arranged in two rows as well as pot 13, a runner 14 and gates 15 which are formed by recessing the lower cavity block 12. The chamber 8 in the cope 1 is opposed to the pot 13, and the cavities 4A in the cope 1 are opposed to the cavities 4B. In a closed state of the cope 1 and drag 2, the chamber 8 leads to the cavities 4A and 4B through the pot 13, the runner 14 extending from the pot 13 as a trench and the gates 15 branching in both sides of the runner 14. On the top surface of the lower wall 11, a circular lower seal block 16 is also provided to surround the lower cavity block 12. The lower seal block 16 is opposed to the upper seal block 5 in the cope 1. The lower seal block 16 is provided with a sealant 7C on the lower wall 11 side surface thereof and a sealant 7D on the cope 1 side surface thereof. Positioning pins 17 are provided at four corners of the lower wall 11 as shown in FIG. 2. Thus, the drag 10 is structured.
A plunger 18 is slidably inserted in the chamber 8. The plunger 18 is provided with a sealant 7E therearound. In the closed state of the cope 1 and drag 2, short size lead frames 19 are held between the upper and lower cavity blocks 3 and 12 at predetermined positions with respect to the cavities 4A and 4B.
FIG. 3 is a plan view showing the short size lead frame 19 which comprises two stripe side members 20 extending in parallel at a distance. The side members 20 are provided with a plurality of holes 21 along the extending direction. Between the side members 20, a plurality of lead patterns 22 are provided, which are structured as follows: A plurality of element mounting pads 23 are supported by supporting arms 24 connecting the element mounting pads 23 to the side members 20. A plurality of inner leads 25 are disposed around each element mounting pad 23. The inner leads 25 lead to outer leads 26. The inner and outer leads 25 and 26 are connected to each other and to the side members 20 through tie bars 27 for supporting these leads 25 and 26. Thus, the lead patterns 22 are structured.
An unit lead pattern for one semiconductor element is defined in an interval M between dashed lines L, wherein the element mounting pad 23 is disposed at the center of the unit lead pattern. A plurality of such unit lead patterns are arranged along the side members 20 at regular intervals M.
A procedure of sealing a semiconductor element with resin will be described. In a pretreatment, semiconductor elements are mounted on the element mounting pads 23 and electrically connected with the inner leads 25 through bonding wires. In this pretreatment process, after the finish of treatment of one of the semiconductor elements, the short size lead frame 19 is moved by one pitch M by using the holes 21 of the side members 20 to treat next one of the semiconductor elements, and thus the treatment is repeated.
The short size lead frame 19 thus pretreated, which is smaller in size than the lower cavity block 12 as shown in FIG. 2, is positioned on the lower cavity block 12 in a manner that each semiconductor element on the element mounting pad 23 is located in the center of each cavity 4B and then held by the cope 1 and the drag 2 clamped by a clamp machine (not shown). Thereafter, preheated tablet resin is put in the chamber 8. The sealant 7A to 7E completely seal between the upper and lower walls 2 and 11, the upper and lower seal blocks 5 and 16, the chamber wall 8A and the plunger 18 so that the inner space enclosed with these is kept airtight.
The plunger 18 is pushed down up to just before coming in contact with the tablet resin and then evacuation through the vacuum air outlet 6 takes place. The resin is heated through surroundings to be melted, so as to be injected into the cavities 4A and 4B through the pot 13, the runner 14 and the gates 15 by further pushing down the plunger 18. Thus, the resin is molded in a shape corresponding to the cavities 4A and 4B at both sides of the lead frame 19 in a region N surrounded with a dashed line in FIG. 3, so that each semiconductor element is sealed in the molded resin.
The conventional vacuum type resin-sealing apparatus structured as hereinbefore described is provided with the sealant 7D only on the drag 11 with respect to the parting plane A--A. Therefore, when this apparatus is employed for sealing with resin a long size lead frame which is longer than the cope 1 and the drag 10, a vacuum cannot be obtained in the inner space enclosed with the cope 1 and the drag 10 since the inner space can not be kept airtight at portions where the long size lead frame is nipped by the cope 1 and the drag 10. If the resin is injected in this state, air left in the chamber 8, runner 14, cavities 4A and 4B and the like is mixed into the resin to become bubbles. This results in decrease of the quality of the molded resin.